This invention relates in general to slitting machines for cutting a relatively wide sheet of material, such as steel, into a plurality of relatively narrow strips. In particular, this invention relates to such a machine which forms at least one relatively shallow furrow in each of the strips to minimize bowing and camber therein after the cutting operation.
Metal materials, such as steel, are often supplied in sheet form for use in manufacturing operations. The thickness of such sheets may vary from several thousandths of an inch to one quarter of an inch or more. For greater convenience and efficiency, sheets of metal are usually supplied in coiled form, wherein the sheet is rolled up lengthwise upon itself in spiral fashion. Often, these coils are supplied in standard widths which are wider than required for the intended manufacturing operations. For example, a coil of steel may be supplied having a width of about six feet, but the manufacturing operations may be intended to handle material which is only about one foot wide. In these instances, the relatively wide sheets must be cut in narrower strips which are usable in these manufacturing operations.
To accomplish this, machines have been provided in the past for cutting the wide sheet of material into a plurality of relatively narrow strips. Such machines usually include some means for supporting the coil thereon and for unrolling the coil at a desired rate. As the coil is unwound, the leading edge of the material is engaged by feed rollers and moved along a path through the machine. A plurality of rotatable slitting discs are provided on the machine for cutting the wide sheet of material into a plurality of narrow strips. The slitting discs are usually supported for rotation about a common axis extending perpendicular to the direction of movement of the sheet. As the material is moved through the machine, the slitting discs cut the wide sheet into the plurality of narrow strips. Then, the cut strips are rewound into individual coils for subsequent use in the manufacturing operations.
Unfortunately, it has been found that the strips of material which are cut from a sheet in this fashion often become bowed after the slitting process. Bowing occurs when the length of the strip is not flat, curving upwardly or downwardly from end to end when viewed from the side. For example, a twenty foot long strip of one quarter inch thick steel has been found to bow up to six inches from end to end after being cut from the sheet. In other words, if one end of such a strip was held down against a flat surface, the other end of the strip would curve upwardly six inches above the surface.
Cut strips of material have also been found to experience camber after the slitting process. Camber occurs when the sides of the strip are non-linear when viewed from above, even when the strip lies flat on a surface (i.e., not bowed). In other words, the sides of the strip arc concentrically from end to end like a flat curved road. When camber occurs, the longitudinal center of the strip at the midpoint thereof is not located on a line connecting the longitudinal centers of the strip at the ends thereof. For example, if a line is drawn between the two longitudinal centers at the ends of a twenty foot long strip of one quarter inch thick steel, the longitudinal center of the strip at its midpoint has been found to be located up to one inch away from the line.
It is believed that bowing and camber are caused by residual stresses created within the sheet of material during its formation. Such formation generally involves hot-mill rolling of the material, followed by water cooling. During the water cooling process, the outer surfaces of the sheet are cooled much faster than the interior regions thereof. This uneven cooling is believed to generate these residual stresses. Although such residual stresses are generally not large enough to adversely affect the overall shape of the uncut sheet of material, they apparently are sufficient to cause bowing and camber when the sheet is cut into relatively narrow strips. In any event, when bowing and camber occur in the magnitudes discussed above, the strip is usually rendered unusable for the intended manufacturing operations. Accordingly, it would be desirable to provide an apparatus for cutting narrow strips of material from a wide sheet which reduces or prevents the occurrence of bowing and camber.